Using active bearings and an appropriate control algorithm, rotors can operate without unbalance forces. This has been theoretically proven and validated experimentally at IMS. Active bearings can displace the centre of rotation. Unbalance induced rotor vibration occur because real rotors cannot be manufactured perfectly and thus never rotate exactly around their main axis of inertia. If active bearings are actively controlled so that the bearing centre orbits with the eccentricity of the rotor, the dynamic forces vanish. The rotor rotates around its main axis of inertia in this case. This technique is applicable even for elastic rotors which do not have a constant axis of inertia.
A multitude of control approaches for driving the active bearings have been investigated at IMS. Rotor system with strong gyroscopy are very challenging in this regard as one has to deal with a speed dependend splitting of eigenfrequencies. Some investigated control approaches are:
- Adaptive feedforward control
- Gain scheduled H∞ optimal control
- Model-free control approach including analytic stability proof
Another research topic is the advancement of active bearings that have so far only been investigated within laboratory applications. The vision is to develop the active roller bearing such that it can be used as a kind of standard machine element. In a first step the integration of the overall setup has been increased using a monolithic manufactured frame which enables functions such as prestressing of actuators.